The present invention relates to an azo monomer and more particularly to a tertiary alkyl, tertiary cycloalkyl or tertiary aralkyl azoalkane which contains only one polymerizable double bond.
In the prior art, unsymmetrical t-alkyl azo compounds are taught in U.S. Pat. Nos. 3,993,609, 4,028,344 and 4,007,165. Although some of these patents teach broadly that double bonds can be present, none of them, however, teach that such double bonds, if present, can be copolymerized. The azo monomers of the present invention do not come within the scope of this prior art.
German Pat. No. 1,055,240 teaches symmetrical polymerizable azo compounds which contain a polymerizable double bond on each side of the azo function. The compound of the present invention does not come within the scope of this prior art because the compound of the present invention is an unsymmetrical azo compound containing only one polymerizable double bond per molecule that has some unobvious advantages over the symmetrical compounds of the prior art. Since the symmetrical azo compounds of the German patent have two double bonds, they can act as crosslinking agents by copolymerizing with two different growing chains. This leads to high molecular weight crosslinked polymers which are very difficult to work with as was experienced in the copolymerization of vinyl acetate with diallyl 4,4'-azobis(4-cyanovalerate) prepared from 4,4'-azobis(4-cyanovaleroyl chloride) and allyl alcohol. This was not a problem when methyl methacrylate was copolymerized with 2-(methacryloxy)-ethyl 4-t-butylazo-4-cyanovalerate (called MEBC) in Example 4, infra. This German patent, only teaches one method of preparing copolymers from their polymerizable azo compounds, that is, the copolymer of the azo compound and a vinyl monomer is prepared under conditions such that the azo group is retained in the copolymer.
R. Kerber, O. Nuyken and R. Steinhausen, Makromol. Chem. 177, pp. 1357-1371, (1976) synthesized unsymmetrical aryl-azo monomers. These aryl-azo monomers were copolymerized with styrene to form azo containing polystyrene copolymers that were grafted with acrylonitrile to form polystyrene-polyacrylonitrile graft copolymers. The aryl-azo monomers of Kerber, et al. are different from those of the present invention since the azo monomers in the present invention are tertiary-alkyl, tertiary-cycloalkyl or tertiary-aralkyl azo compounds. This is a significant difference since aryl-azo groups are the highly chromophoric functions of the classical azo dyes while alkyl-azo groups are not. Thus, Kerber's azo compounds are necessarily highly colored and can impart undesirable color bodies into polymers whereas the azo monomers of the present invention do not.
Kerber's aryl-azo compounds all contain two alphacyano moities which limits their temperature activity and presents toxicity problems both in the azo itself and its decomposition fragments while the alkyl-azo monomers of the present invention do not have these drawbacks.